Molecular and Electronic Structure of ä-Valerothiolactone

DUGARTE, NAHIR Y.; ERBEN, MAURICIO F.; BOESE, ROLAND; GE, MAO-FA; YAO, LI; DELLA VEDOVA, CARLOS O.

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Año: 2010 vol. 114 p. 12540 - 12547

1089-5639

The crystal structure of the six-member heterocyclic δ-valerothiolactone (1-thiocycloalkan-2-one) compound has been determined by X-ray diffraction at low temperature, revealing that its skeleton adopts a half-chair conformation. The conformation around the thioester group is almost planar with an anti orientation of the C=O double bond with respect the S-C single bond [C(2)-S(1)-C(6)-O(1) ) 176.26(8)°]. The skeletal parameters, especially valence angles  [∠C5-C6-S ) 121.19(6)°, ∠OdC6-C5 ) 122.25(8)°, ∠C6-S-C2) 106.80(4)°], differ from those typically found in acyclic thioester compounds, symptomatic of the presence of strain effects. The conventional ring strain energy was determined to be 7.5 kcal/mol at the MP2/6-311++G(d,p) level of calculation within the hyperhomodesmotic model approximation. Moreover, the valenceelectronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.35, 9.50, and 11.53 eV denote ionizations related with the nS, nO, and πCdO orbitals, respectively, demonstrating the importance of the -SC(O)- group in the outermost electronic properties.